There is a continual need for new food preservatives bearing new and useful properties. Further, there is growing interest in replacing traditional “chemical” food preservatives with effective “natural” preservatives, especially those that inhibit pathogenic microorganisms. In this regard, considerable research has been conducted on bacterial peptides, known as bacteriocins, that are often heat stable and have antimicrobial activity. Two such bacteriocins that are commercially produced for use as food preservatives are nisins A and Z and pediocin PA-1. Nisin has been given the status of Generally Recognized As Safe For Human Consumption (GRAS) by the United States FDA. Nisin and pediocin PA-1 have broad spectrum activities against gram-positive bacteria, affecting both pathogenic and spoilage microorganisms in food products.
Recent years have seen major advances in the development of microbial metabolites with antagonistic activities towards spoilage and pathogenic microorganisms associated with food. There now exists many antibacterial compounds, but only a few have been fully characterized and evaluated for food use. Additionally, consumer emphasis is now on minimally processed foods that are natural and preservative free. Because of this, there is considerable resistance to the use of chemical additives as food preservatives. Because of problems of antibiotic resistance, the use of antibiotics that can be used for therapeutic purposes may not be used for food preservation. Other biological inhibitors produced by microorganisms are currently being investigated for use in foods. Of particular interest are those antibacterial substances such as bacteriocins that are produced by Lactic Acid Bacteria (“LAB”).
Bacteriocins, which are anti-bacterial peptides and proteins produced by LAB as normal by-products of their metabolism, are potentially very attractive natural preservatives. Many LAB are well-established, industrially important bacteria that include the genera Lactococcus, Streptococcus, Pediococcus, Leuconostoc, Lactobacillus and Carnobacterium. They have been used for the production of fermented foods that have been consumed safely for many decades. Given their status as “safe” microorganisms, they are a particularly suitable source of natural antimicrobials, such as bacteriocins, for use in foods.
Bacteriocins can have a broad or narrow spectrum of antibacterial activity, and they are not lethal to the cells that produce them. Bacteria protect themselves from the lethal effects of their own bacteriocins by the production of immunity proteins. There are distinct classes of bacteriocins produced by LAB:
A. Lantibiotics—which are small peptides of less than 5 kDa that contain unusual substituents, such as lanthionine, dehydroalanine, dehydrobutyrine and β-methyllanthionine. Examples include nisins A and Z, lacticins 481 and 3147, carnocin U149 and lactocin S.B. Non-lantibiotic peptides—which are small peptides of 10 kDa or less and can be subdivided as follows: (i) listeria-active peptides e.g. pediocin PA-1, leucocin A and sakacin A.; (ii) poration complexes consisting of two proteinaceous peptides e.g. brochocin C and lactacin F.; and (iii) thiol-activated peptides requiring reduced cysteine residues for activity e.g. lactococcin B.C. Large heat-labile proteins—which are larger proteins generally having a molecular weight greater than 31 kDa e.g. helveticin V-1829.
Notwithstanding the usefulness of the above described natural preservatives, a need still exists for lactic acid bacteria and their bacteriocins that are capable of controlling pathogenic and spoilage bacteria in specific food products.